Not Applicable.
Not Applicable.
1. Field of the Invention
The present invention relates generally to a releasable connection for a downhole assembly and more particularly to a releasable connection connecting a downhole tool to a coiled tubing string and still more particularly to a connection electrically actuated from the surface to disengage the coiled tubing string from a stuck downhole drilling tool or bottom hole assembly (BHA).
2. Description of the Related Art
Increasingly, the drilling of oil and gas wells is no longer a matter of drilling a vertically straight bore hole from the surface to the desired hydrocarbon zone. Rather, technology and techniques, such as directional drilling, have been developed to drill deviated, lateral or sometimes upwardly sloping boreholes. It is often not economically feasible or practical to use jointed drill pipe in extended reach wells. Therefore, tools and methods have been developed for drilling bore holes using coiled tubing, which may include one or more lengths of continuous, unjointed tubing spooled onto reels for storage in sufficient quantities to exceed the maximum length of the borehole. The coiled tubing may be metal coiled tubing or, using more current technology, composite coiled tubing.
In well drilling applications, a BHA, having various components, such as a downhole motor, steering assembly, and bit, is connected to the end of a coiled tubing string for drilling the borehole. Circumstances can arise in which it is desirable to disconnect the tubing string from the BHA, such as, for example, when the BHA gets stuck in the borehole during drilling and the tubing string must be disconnected from the BHA in order to facilitate fishing, jarring, or other operations for retrieving the BHA.
In using jointed pipe for drilling, torque can be applied to the threaded connections to actuate traditional disconnect means to disconnect the BHA. However, when using continuous tubing, such as metal or composite coiled tubing, torque can not be applied to disconnect the tubing string from the BHA, and an axial disconnection means must be utilized. Pre-installation of one or more axial release devices between the tubing string and the BHA assembly can provide a means to disconnect the coiled tubing string downhole if and when disconnection becomes necessary.
A variety of axial disconnect means have been used to disconnect a coiled tubing string, some of which use hydraulic or electrical lines that extend from the surface to the disconnect means to actuate a piston and cause release. One such device, described in U.S. Pat. No. 5,984,006, includes an emergency release tool that can electrically release coiled tubing from one or more downhole tools. The release tool includes a releasable slip forced against the coiled tubing by a loading nut. The coiled tubing is released by sending an electrical signal to a downhole release means. Once activated, the release means forces a piston upward until the piston engages a slip housing. The slip housing is coupled to the loading nut. The release means continues to force the piston and, consequently, the slip housing upward to separate the loading nut from the releasable slip, thereby disengaging the releasable slip from the coiled tubing.
Another such means, described in U.S. Pat. No. 5,323,853, includes redundant releasing mechanisms depending alternatively on either hydraulic or electrical actuation of a piston. The additional lines and cables, which run inside the well bore that are required to actuate the release, have the disadvantage of creating an obstruction to fluid flow during normal drilling operations.
Another type of known release means depends for actuation on directing fluid flow so as to create backpressure and actuate a piston. U.S. Pat. No. 5,718,291 describes one such release mechanism that depends for actuation on either the use of backpressure created by flow through the mechanism, or if flow is prevented, the use of built-up pressure within a passage in the mechanism. In the first mode, backpressure created by flow through a restrictor above a shiftable sleeve overcomes a biasing spring to move the sleeve through a J-slot assembly until a passage is obstructed. Thereafter, pressure buildup in a second passage overcomes a shear pin, causing a piston to move and release dogs that lock two segments of the mechanism together. If flow is prevented, pressure buildup in the second passage causes the piston to move against the shifting sleeve to overcome the force of the spring and selectively move the sleeve through the J-slot assembly. A disadvantage of this release mechanism is that aligning the sleeve properly to engage the top of the J-slot assembly is cumbersome, requiring that pressure be created and removed by turning pumps on and off from the surface.
Still another conventional release device depends for actuation on dropping a ball into a well from the surface, sealing a flow passage, and building up pressure behind the ball to cause a disconnection. One such ball-drop release device is described in U.S. Pat. No. 5,419,399 and includes a housing with a slideable piston disposed within and releasably connected to the housing by shear screws. A ball is dropped into the well from the surface to seat with the upper end of the piston and block the flow passage, thereby creating pressure on a mandrel of the piston sufficient to overcome the shear screws. The mandrel moves downward such that keys align to fit into annular grooves on the mandrel to disengage notches, allowing the tubing to be disconnected from the drilling apparatus. A disadvantage of this device is that the operator must pull back or agitate the device to cause the keys to drop into the grooves should they fail to do so.
A further ball-drop release device is described in U.S. Pat. No. 5,526,888 and includes an upper and lower housing insertably connected and locked together by latch blocks, a slotted piston that operates the latch blocks, a pilot piston, and a lock-out mechanism operated by movement of the pilot piston. A sealing ball is dropped into the well and seats with the pilot piston to create a pressure differential sufficient to overcome shear pins, thereby allowing the pilot piston to axially shift downward. Movement of the pilot piston releases a lock-out mechanism such that the slotted piston extends axially to retract the latch blocks and thereby disconnect the upper and lower housings.
The present invention overcomes the deficiencies of the prior art.
The disconnect assembly of the present invention connects two portions of a downhole assembly having a downhole apparatus attached to a coiled tubing string. The disconnect assembly includes a first housing connected to one portion of the downhole assembly and a second housing connected to another portion of the downhole assembly. The housings are releasably connected by a release assembly. The release assembly is coupled to a drive train on a motor by a connection transferring rotational motion into translational motion. The release assembly includes locking members having a connected position engaging both housings and a disconnected position disengaging one of the housings. The motor is connected to the surface by conductors extending through the coiled tubing whereby the motor may be actuated from the surface to move the release assembly between the connected and released positions.
One embodiment features a selectively actuated disconnect assembly comprising: an outer housing; an inner housing having a cavity and disposed within the outer housing; a locking assembly disposed within the cavity for releasably locking the inner housing with the outer housing; an electrically actuatable power source housed in the cavity for actuating the locking assembly; a drive train coupled to the power source; and a connection coupling the locking assembly with the drive train for engaging and disengaging the locking assembly. In one embodiment of the invention, the disconnect assembly is disposed in a downhole assembly having a bottom hole assembly attached to a coiled tubing with conductors extending to the surface to an electric motor selectively actuatable from the surface; a lead screw having first and second ends and being coupled at the first end to the electric motor; a lead sleeve coupled to the first end of the lead screw and connected to a release shaft by a universal joint, the release shaft having an exterior surface with annular grooves and a plurality of locking pins disposed in transverse bores in the inner housing with one end disposed in the release shaft grooves in the unlock and released position and another end disposed in internal grooves about the outer housing in the locked and connected position.
The present invention also includes methods of disengaging a bottom hole assembly from coiled tubing, a method comprising: actuating an electric motor via a command signal; rotating a lead screw that is coupled to the electric motor and to a release shaft; axially moving the release shaft a distance sufficient to align grooves on the release shaft with the inner ends of radially extending pins, and moving the release shaft to cam the other ends of the pins out of the outer housing grooves.
In one embodiment of the present invention, the disconnect assembly used to release a portion of the downhole assembly above a stuck point. The disconnect assembly of the present invention is most useful in coiled tubing drilling operations. A plurality of these disconnect assemblies can be deployed at different positions in the downhole assembly. This allows selective actuation of one or more of the disconnect assemblies in the downhole assembly to release that disconnect assembly which is the closest to the stuck point, thereby minimizing the length of the downhole assembly to be fished out, greatly increasing the chance of a successful fishing operation, and minimizing the damages to the BHA components during fishing.
A feature of the invention is that the disconnect assembly has a common electrical and mechanical connection. Further, the disconnect assembly is selectively reconnectable. This allows an operator to activate the disconnect assembly in an attempt to remove the downhole assembly. If the downhole assembly remains stuck despite the disconnect assembly having been activated, the stuck point for the downhole assembly is likely up-hole from the disconnect assembly. The operator can signal the disconnect to reconnect. The operator can then activate a disconnect assembly up-hole from the initially activated disconnect assembly. Another feature of the invention is that it does not use a taper wedge lock mechanism, which is a simple and common employment for this type of application. However, a taper wedge lock tends to seize up and become self-locking after a long period of down hole vibration in drilling, which makes release operation difficult, if not impossible. The disconnect assembly of the present invention utilizes locking pins and a release shaft. Being round in geometry, it minimizes the chance of being self-locking to prevent release.
Thus, the present invention comprises a combination of features and advantages which enable it to overcome various deficiencies of prior devices. The various characteristics described above, as well as other features, will be readily apparent to those skilled in the art upon reading the following detailed description of the preferred embodiments of the invention, and by referring to the accompanying drawings.